"He spoke to the issue of racism within police forces in the United States," is correct usage. I italicized "spoke to the issue of" because it is the whole phrase that replaces "about." Usually, "to" cannot replace "about" in normal, everyday speech or writing.
As to your second question, one does not generally speak "as to" something, but uses it as I have in this sentence.
I changed "the police force" to "police forces," because almost every city in the United States has its own, separate police department (there are more than twelve thousand of them).
[The following is off-topic but needs to be addressed, in my opinion.]
Racism is a problem in some departments and not in others. As a former dispatcher for a small university-town police department and later the Criminal Justice Planning Director for four counties in northwestern California, I can assure you that virtually every police department in the U. S. is actively working to reduce racism in their ranks, especially in response to the horrible abuses we all have seen on television. Please remember that most police officers are not racist and work hard to maintain a fair and impartial attitude towards all citizens. It is only a relatively small percentage of officers and departments that have tarnished the good work of everyone in law enforcement.
If you have the opportunity, I encourage you to seek a department where you can "ride along" with an officer during his or her shift to get a better idea of what these highly trained men and women deal with on an everyday basis. You might be amazed at the abuse they not only tolerate and ignore but respond to with courtesy and respect, abuses that would make an ordinary civilian so angry as to act out in a way that would not be appropriate. Once you have witnessed the extraordinary self-control and professionalism of most police officers, you will be less likely to think in global terms of "the police force" in the United States. Thank you for your question and for raising the issue.